Introduction to Johne’s Disease

Johne’s disease was first identified in the U.S. dairy
industry over 100 years ago, yet many producers are
still unfamiliar with this serious, infectious disease.
Johne’s disease, is a chronic, infectious disease which
affects domestic and exotic ruminants including dairy and
beef cattle, sheep, goats, cervids and camelids. It has been
called one of the most serious diseases affecting cattle
today.

The disease is caused by Mycobacterium paratuberculosis,
a slow-growing bacteria. This bacterium invades the
animal’s small intestine causing a thickening of the intestinal
wall, reducing the absorptive capability of the intestine.
According to researchers at Michigan State University,
the bacteria are taken up by specialized cells in the small
intestine. As the body tries to rid itself of these bacteria, the
immune response causes a thickening of the intestinal
lining, preventing it from functioning normally. This leads
to poor absorption of nutrients and eventual diarrhea. As a
result, although animals may be feeling and eating well,
they begin to lose weight.

Because of the slow, progressive nature of the infection,
signs of Johne’s disease may not be seen until years after the
onset of infection. The clinical signs of Johne’s can be easily
confused with several other diseases, including intestinal
Parasitism, malnutrition, salmonellosis, hardware disease
and winter dysentery. The most definitive way to determine
the presence of Johne’s is through testing.

Clinical signs in cattle, include profuse watery diarrhea,
weight loss, and lowered milk production. Appetite
will stay the same or increase. Some animals may have a
low-grade fever, and develop edema under the jaw (bottle
jaw).

Johne’s disease in a herd is said to be a silent disease. It
may loom in the herd for years before a clinical case surfaces.
The presence of infection in the herd is hard to detect
until the disease has progressed to the second or third stage.

All cases of Johne’s ultimately progress through the
four stages of development until the animal dies or is
culled.

Stage 1 is silent, subclinical and non-detectable. Infected calves and animals younger
than two years of age, or those exposed to a small dose of bacteria, which do not
show symptoms, are in this category.

Stage 2 animals are generally older heifers
or adults that may appear healthy. However, these subclinical shedders are generally
passing enough organisms in their manure to be detected by fecal culture test. These
animals pose a risk to others in the herd by contaminating the environment.

Stage 3 animals have visible symptoms of Johne’s disease. They have acute or intermittent
watery diarrhea, weight loss, and a drop in feed efficiency and milk production.
Intermittent signs at this stage usually progress to more severe infection.

Stage 4 is the end of the disease process. Most animals appear very thin, with fluid diarrhea.
Animals may progress from Stage 2 to Stage 4 in just a few weeks.

The M. paratuberculosis bacteria are usually introduced to
dairy herds through the purchase of infected though
clinically normal cattle (Stage 2). Once the bacterium is
introduced to the herd, it can spread quickly through contaminated
feces.

The time from initial infection to onset of clinical signs
(diarrhea and weight loss) is generally two to five years.
Calves are the most susceptible to infection with the Johne’s
organism, especially in the first few weeks of life. Animals
greater than one year old may acquire M. paratuberculosis
infection but are more resistant to infection than young
calves.

The South Dakota Extension Service reports that animals
infected with M. paratuberculosis eventually shed the organism
in the manure, with the number of organisms increasing
over time. Cattle showing clinical Johne s disease shed a
tremendous number of organisms into the manure, resulting
in heavy environmental contamination.

The vast majority of infections in young animals are
acquired by ingestion of M. paratuberculosis. This happens
when they consume manure containing the bacterium.
Sucking on manure contaminated teats on the udder of their
mother, licking contaminated bars in the stall where they
are born, or being housed in a location where they have
access to manure from the adult herd are all ways young
animals have opportunities to ingest this bacterium.

A second method of exposure is by drinking infected
milk. M. paratuberculosis is excreted in the milk of infected
lactating animals, particularly when the infection is in the
more advance stages. When colostrum is pooled among
animals, there is a risk of spreading the bacteria from one
infected animal to several newborn calves.

Animals that spend a lot of time with their mothers and
nurse naturally have the highest risk of becoming infected.
On dairies where calves are normally removed from cows
and housed separately, the practice of feeding whole milk
instead of artificial milk replacers can result in the spread of
A third, but less common, route of infection is in utero. In
later stages of the disease, the bacterium can spread from
the small intestine to other parts of the body. In advance
stages of the disease, the bacterium can travel to the fetus of
a pregnant animal.

Research conducted at Michigan State University in 1999
predicted that 55 percent of Michigan’s dairy herd
have two or more animals carrying Johne’s disease. Likewise,
in Wisconsin, research in 1994 found that an estimated
34 percent of the dairy herds had indications of the disease.
Because only an estimated 1 percent of the infected
animals actually exhibit clinical signs, researchers refer to
an iceberg effect when diagnosing the disease. What
actually surfaces is only the tip of what is in the herd. For
every clinical animal, there are 5 to 15 infected animals at
the subclinical level.

Increasing awareness of Johne’s disease among producers
and veterinarians is key in helping control this serious
disease. In-depth information regarding Johne’s will be
presented each month in this bulletin.
Upcoming issues will address control measures on the
farm, the economic impact of Johne’s disease, management
strategies and testing procedures. If you have additional
questions please contact AntelBio at 1.800.631.3510.

Board of Regents, the University of Wisconsin System School of Veterinary
Medicine (1999); Pathogenesis of Johne s Disease.
Indiana Board of Animal Health (2000) Commonly Asked Questions about
Johne s disease.

South Dakota Extension Service Johne s Disease in the Beef Herd.
Ohio Department of Agriculture (2000) Johne s disease.
Michigan State University ANR Communications Johne s Disease Target of
Control Program. April 2000.